In Tiger Lily case of Mysterious ways you need to guess which two substances to test from the hair.

The possible substances to test are: Amatoxin, arsenic, atropine, botulinum A, cyanide, plutonium, maitotoxin, mercury, polonium, ricin, sarin, strychnine, tetrodotoxine, thallium, xanthium

And the symptoms were, from the doctor's log: "First time Caeleb came by in a long time. Patient presented with muscle pain in the thighs and gastrocnemius, as well as plantar numbness. He also exhibited hair loss of the scalp. Patient also reported nausea and abdominal pain. Xrays and bloodwork came back normal (slightly high LDL and glucose). Potentially stress related as patient reports overwork and fatigue. Placed patient on medical leave. Will conduct more tests after a few days rest."

Try to search the symptoms for the poisons in the Internet.

The most interesting symptoms were loss of hair and muscle aches. Specifically "plantar numbness" and "gastrocnemius muscle pain".

Searching through all the poisons, following ones are known to cause hair loss: plutonium, polonium and thallium.

Search each one with their name and plantar numbness gastrocnemius.

See if they get any mentions.

Thallium